'Amr bin Shu'aib on the authority of his father and grandfather reported:
Messenger of Allah (ﷺ) said, "It is not permissible for a person to sit between two people without their permission."[At-Tirmidhi]. (ES)
App reference (ES): Book 5, Hadith 16 (ES)
Arabic/English book reference (ES): Book 5, Hadith 829 (ES)